I recently got a black mystery (apple) snail. The same day I got him I also got mondo grass from the same tank. I should have known this was a bad idea but I didn't see any eggs on the plants. I rinsed them and put them in a fishbowl with water and my tetras so I could change the tank water before adding plants. I added the plants and put the tetras back in the tank. The same day my sister got a Betta and put it in that fishbowl, with new water and fake plants. A couple weeks later snails started showing up in her bowl. But none showed in my tank. About three weeks after this she decided to put her Betta in my five gallon with the gravel from her bowl + my old gravel. Then i got a ten gallon to accommodate for my Betta, three tetras and growing snail. Now it's been two more weeks and the five gallon tank is filled with baby snails. I've taken 60 of them out and put them in a Tupperware container with algae till I can release them. There are still no snails in my tank. Where are all the snails coming from? Why can't I see the eggs. How is it possible for that many eggs to be stuck to two mondo grass plants? Is it possible that my ten gallon has snails but my Betta and big snail could be eating them?

You really shouldn't take fish out for water changes, especially tetra, they stress very easily.
Snails eggs can get stuck to everything.
Do they look like baby mystery snails? They will lay their eggs above the water line, and it's possible your snail was pregnant when you got her.

Releasing them is a humungous NO-NO as its introducing a non native species into the environment. Non native species can and will cause all sorts of environmental havoc, including harming the native wildlife and even causes native species to go extinct.

I highly recommend you find other ways to cope with your snail problem.